Rory
There are only 8 managers in the whole game with 10000, however if this number of managers still increases I do not think that expanding the range solves the problem.
Rory.
Once you hit 10k it is relatively easy to remain there because of the 100 rep point bonus for finishing top 2 places in Elite as mentioned by Sam.
Also, if I hit 10k and then retire my team I will remain there forever. At least 3 of the 8 you mention are retired accounts but admittedly they all belong to arguably the best manager to have played new iGP. I do think the list will continue to grow.